Balanced variable reactance device



y 1949- R. v. LANGMUIR ET AL 2,471,155

BALANCED VARIABLE REACTANCE DEVICE Filed June '7, 1946 Patented May 24, 1949 2,471,155 BALANCED VARIABLE REACTANCE DEVICE Robert V. Langmuir and Philip H. Peters, Jr.,

Schenectady,

N. Y., assignors to General Electric Company, a corporation of New York Application June 7, 1946, Serial No. 674,971

9 Claims. 1

This invention relates to variable reactances for high frequency oscillating systems, and more particularly to a novel apparatus which permits simultaneous adjustment of both the inductance and capacitance of a system in such a manner that those parameters are always electrically balanced with respect to a fixed electrical reference point, such as a ground connection of zero voltage.

For the purpose of tuning high frequency oscillating systems it has been a practice heretofore to provide a mechanically variable reactance in which both the inductance and the capacitance may be simultaneously decreased or simultaneously increased by the motion of a single movable member. The simultaneously variation of the two has been found to result in a more convenient tuning of the system over a greater range of frequencies. In one exemplary construction known heretofore, the inductance and capacitance are provided by juxtaposed parallel disks having sector-shaped cut-out portions leaving corresponding sectoral ring portions on the periphery of the disks. The disks are interleaved on a common axis of rotation in such manner that relative rotation thereof effects an increase or decrease of the capacitance between the disks and a like simultaneous increase or decrease of the inductance formed by the peripheral ring portions.

A notable disadvantage of such arrangements lies in the fact that when they are employed as tuned circuits in which standing waves are set up the reactance presents no electrically neutral point which is fixed for all positions of the movable members, i. e., the point of zero high frequency voltage shifts about on the inductive portion as the movable member is operated. That disadvantage can be particularly inconvenient in certain types of electrical circuits, for example, those employing push-pull networks in which the various voltages and currents must be balanced against a common electrical reference point.

Accordingly, it is the general object of this invention to provide a variable reactance having simultaneously adjustable inductive and capacitative components in which those components are electrically balanced with respect to a fixed electrical reference point for all values of reactance.

Features of the invention desired to be protected are pointed out in the appended claims. The invention itself, together with further objects and advantages thereof may best be understood from the following description taken in conjunction with the accompanying drawing in which Fig. 1 represents a device embodying a variable reactance in accordance with the principles of the invention, while Fig. 2 represents schematically an oscillating circuit in which the invention might find employment.

Referring to Fig. l, the invention is shown as comprising a plurality of fixed plates, I through 4, having rectangular cutout portions 5 and 6, such that the plates present a substantially C-shaped configuration as shown. The configuration is bounded, as will be apparent from the drawing, by a loop comprising a vertical memher 1, horizontal arms 8 and 9, and extended fiat portions Ill and II of substantial area projecting toward each other but being separated by the gap formed by the rectangular cutout portions 6. Within the interspaces between the plates I through 4 there is provided a slidably mounted plurality of preferably conductive plates l2, l3 and M of substantial area, these latter plates being slidably positionable throughout the length of the interspaces between the plates I through 4 in such a manner that in one extreme position they are completely within the interspace between the portions l0 and H and in the other extreme position they are completely within the area comprised by the rectangular cutout portion 5 of the plates I through 4. It will be understood that by the expression substantial area as applied to portions I0 and II and plates l2, l3 and I4 is meant an area sufiicient to provide whatever value of capacitance is desired for the device. The capacitance, and thus the area, will be determined by the particular inductive and capacitative range desired for the reactances.

The plates l2, l3 and I4 may be slidably mounted by any suitable means, such as by means of the insulating carrier members l5 which slide on a track IS on the base I! which may be of conductive material such as copper, and which may conductively interconnect plates I through 4. The plates l2, l3 and M are spaced and supported in insulated relationship from plates I through 4 by means of the cross arm l8 which rests on carrier members 15. Any suitable means for moving the plates !2, l3 and M in reciprocating motion on the tracks l6 may be provided although for purposes of illustration there is shown a threaded driving rod l9 which threadedly engages screw 20 on one of the carrier members [5 and which is secured against longitudinal movement by flange or washer members 2i and 22 abutting against end plate 23. By

means of a thumb screw 24 the threaded rod I9 may be operated in reciprocating fashion either manually or by suitable power devices (not shown). The plates I through i may be closed at their ends by means of conductive end plates 23 and 26 and top plate 2'! conductively connected to the plates I through 4 and forming an enclosure therefor.

For the purposes of illustration of one exemplary employment of the device there is shown a magnetron 28 which may be of the conventional split anode type. Each of the anode leads 29 is connected to one of the portions Ill and II by preferably short connecting leads 29' which have a minimum of capacitance and inductance of their own. When properly energized, as hereinafter set forth in greater detail, the magnetron will oscillate with the described reactance as a tuned external circuit, the oscillating frequency of the magnetron being dependent upon the reactance value as determined by the position of the slidable plates 12, I3 and I4.

It will be understood that the variation of the reactanc'e of the device will beeffected in operation in some such manner as follows: The inductance will be primarily determined by the area bounded by the movable plates I2, is and I4, vertical member "I and the arms 8 and 9. As the members 52, I3 and I l are moved to the lefthand end of the device that area will become progressively smaller. The eiiective inductance of the reactance is thereby decreased. The capacitance of the device will be primarily determined by the capacitance between the slidable plates I2, 13 and M and the flat portions It? and II of the fixed plates I through t. As the slidable plates I2, I3 and M are moved to the left, the effective capacitance will obviously be decreased inasmuch as the plates l2, I3 and I 4 are withdrawn from proximity to the portions Iii and II. It will be apparent, therefore, as the plates I2, I3'and I4 are moved 'to the left, both the inductance and capacitance of the reactor will simultaneously decrease and conversely as the plates I2, I3 and I4 are moved to the right the inductance and capacitance will simultaneously increase. It will also be observed that because of the geometry of the device a horizontal transverse plane through the central portion of both setsof plates may 'bedrawn in such manner that both the inductance and thecapacitance of both the fixed and movable members are symmetrically distributed on either side of that plane. Such plane is indicated by the line 38 of Fig. 2. This will obviously be the'case for all positions of the slidable members 12, I3 and It. Plates I through 4, I2, 13 and I4 will haveoppo'site halves of their surfaces on opposite sides of that transverse plane.

Referrin now to Fig. 2 in which corresponding portions of "Fig. 1 are similarly identified, there is shown as an'example of one use of the aforedescribed reactance, an oscillating circuit comprising the magnetron 3i, a variable reactance of the type heretofore described, and a suitable output circuit in the form of the parallel transmission line32 which'c'onducts energy from the oscillating circuit to any suitable external utilization'circuit (not shown). The magnetron 31 may be of any of the conventional types such as the split anodetype. For purposes of illustration it is shown as comprising the anodes 33 and 34 energized by any suitable source of direct potential 35, and a thermionic cathode 36 energized li'iight oscillate with those leads as the sole external tank circuit, those leads are made no longer than is necessary to connect the magnetron to the reactance. The line 32 may comprise conductors 3B and 39, each connected respectively to the points 40 and A l on the inductive portion of the reactor. It will be understood that the points 40 and l! may be chosen at any suitable points on the inductance or the capacitance depending upon the voltage desired to be imposed 011 the line 32. For balanced condition such as required in certain push-pull type connections it may be'desirable'to choose the p'o'ints l-fl and i l -symmetrically on opposite sides of the center line '39 which forms the electrical neutral plane 'of the device. The central portion of the inductance may begrounded as shown at a point once'hter line 30.

It will be understood that because of the reactive changes effected by sliding motion of the movable plates I2, I3 and I4, the magnetron 31 will "oscillate at 'diiierent frequencies depending upon the position of the slidable members.

It "will be seen that in the foregoing arrangement there is provided'a variable reactance which accomplishes the aforementioned objects of the invention. The electrical characteristics of the device are balanced about the central plane con sidered as an electrical reference point, while at the same time the inductance and capacitance will 'be simultaneously increased or simultaneously decreased by the motion of a positionable member. At the same time advantageous features lie in the fact that there are no sliding contacts, with the result that resistances are minimized to 'give the Q 'of the circuit a maximum value. Because of "the balanced nature of the arrangement it will be readily e'mployable in many circuits known to the "art where such balance is necessary.

While we have 'shownand described a particular embodiment of our invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from our invention in its broader aspects and we, therefore, aim in the appended claims 'to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the Unitedstates is:

I. A variable reactance comprising a conductive 'pl'ate having a loop constituting an inductive portion and surfaces of substantial area on opposite "ends of said loop constituting a capacitative portion, said loop and said surfaces being symmetrically distributed with respect to a central transverse plane through said plate, a positionable niernbe'r of substantial 'area'having opposite halves symmetrically positioned on opposite sides of said transverse plane and juxtaposed in symmetrical relation to said loop and said surfaces, and means for moving said positionable member parallel to and in proximity tosaid-plat-e, whereby the :su'rface of said positionabl'e member may "be juxtaposed in varyin proportions to said loop and said surfaces.

2. A variable reactance comprising a conductive plate having a loop constituting an inductive portion and surfaces of substantial area on opposite ends of said loop constituting a capacitative portion, a positionable member of substantial area juxtaposed to said plate in symmetrical relation with respect to said surfaces, said loop, said surfaces and said positionable member being symmetrically positioned with respect to a central transverse plane through said plate whereby electrical voltage and current relations in said plate are electrically balanced with respect to said transverse plane, and means for moving said positionable member parallel to and in proximity to said plate whereby the surface of said positionable member may be juxtaposed in varying pro-portions to said loop and said surfaces.

3. A variable reactance comprising a conductive plate having a loop constituting an inductive portion and surfaces of substantial area on opposite ends of said loop constituting a capacitative portion, said loop and said surfaces being symmetrically distributed with respect to a central transverse plane through said plate, a po-; sitionable member of substantial area having opposite halves symmetrically positioned on opposite sides of said transverse plane and juxtaposed in symmetrical relation to said loop and said surfaces, and means for moving said positionable member parallel to and in proximity to said plate to juxtapose the surface of said positionable member in varying proportions to said loop and said surfaces whereby motion of said positionable member in one direction effectively decreases both the inductance and capacitance of said reactance simultaneously and motion in the other direction simultaneously increases both the inductance and capacitance of said reactance simultaneously.

4. A variable reactance comprising a substantially C-shaped conductive plate having a loop constituting an inductive portion and surfaces of substantial area on opposite ends of said loop constituting a capacitative portion, said loop and said surfaces being symmetrically distributed with respect to a central transverse plane through said plate, a positionable member of substantial area having opposite halves symmetrically positioned on opposite sides of said transverse plane and juxtaposed in symmetrical re-l lation to said loop and said surfaces, and means for moving said positionable member parallel to and in proximity to said plate to juxtapose the surface of said positionable member to varying proportions of said 100p and said surfaces whereby motion of said positionable member in one direction effectively decreases both the inductance and capacitance of said reactance simultaneously and motion in the other direction simultaneously increases both the inductance and capacitance of said reactance simultaneously.

5. A variable reactance comprising a plurality of parallel conductive plates each having a loop constituting an inductive portion and surfaces of substantial area on opposite ends of said loop constituting a capacitative portion, said loop and said surfaces being symmetrically distributed with respect to a central transverse plane through said plates, a plurality of positionable parallel members of substantial area having opposite halves symmetrically positioned on opposite sides of said transverse plane movably positioned within the interspa-ces between said plates and being juxtaposed in symmetrical re lation to said loops and said surfaces, and means for moving said positionable members parallel to said plates whereby the surface of said positionable members may be juxtaposed in varying proportions to said loop and said surfaces.

6. A variable reactance comprising a plurality of parallel conductive plates each having a loop constituting an inductive portion and surfaces of substantial area on opposite ends of said loop constituting a capacitative portion, said loop and said surfaces being symmetrically distributed with respect to a central transverse plane through said plates, a plurality of positionable parallel members of substantial area having opposite halves symmetrically positioned on opposite sides of said transverse plane movably positioned within the interspaces between said plates and being juxtaposed in symmetrical relation to said loops and said surfaces, and means for moving said positionable members parallel to said plates to juxtapose the surface of said positionable members in varying proportions to said loop and said surfaces whereby motion of said positionable members in one direction effectively decreases both the inductance and capacitance of said reactance simultaneously and motion in the other direction simultaneously increases both the inductance and the capacitance of said reactance simultaneously.

7. A variable reactance comprising a plurality of parallel conductive plates each having a loop constituting an inductive portion and surfaces of substantial area on opposite ends of said loop constituting a capacitative portion, a plurality of parallel positionable members of substantial area one of each being positioned in each of the interspaces between said plates in symmetrical relation with respect to said surfaces, said surfaces, said loops and said positionable members being symmetrically positioned with respect to a central transverse plane through said plates whereby electrical voltage and current relation-s in said plates are electrically balanced with respect to said transverse plane, and means for moving said positionable members parallel to and in proximity to said plates whereby the surface of said positionable members may be juxtaposed in varying proportions to said loops and said surfaces.

8. A variable reactance comprising a plurality of parallel conductive plates each having a loop constituting an inductive portion and surfaces of substantial area on opposite ends of said loop constituting a capacitative portion, said loops and said surfaces being symmetrically distributed with respect to a central transverse plane through said plates, a positionable member comprising a plurality of parallel plates of substantial area each having opposite halves symmetrically positioned on opposite sides of said transverse plane and juxtaposed in symmetrical relation to said loops and said surfaces, and mean-s for moving said positionable member parallel to and in proximity to said first mentioned plates to juxtapose the surface of said second mentioned plates in varying proportions to said loops and said surfaces whereby motion of said positionable memher in one direction effectively decreases both the inductance and capacitance of said reactance simultaneously and motion in the other direction simultaneously increases both the inductance and capacitance of said reactance simultaneously.

9. A variable reactance comprising a plurality of parallel substantially C-shaped conductive plates each having a loop constituting an inductive portion'rand surfaces :of substantial area on opposite 'ends of said =loop constituting a capacitative portion, said loop and said surfaces being symmetrically distributed with respect to a central transverse plane through said plate, a plurality of parallel positionable members of substantial area having opposite halves symmetrically positioned-'onopposite sides of said transverse plane and juxtaposed in symmetrical relation'to'said loopsan'd said surfaces, and means for moving said positionable members parallel to and in "proximity to said plates to juxtapose the surface of said positionable members in Varying proportions to said L'IOQDSaIld "said surfaces whereby motion of said positionable members in one direction efiectivelydecreases boththe inductance and [capacitance of said reactance simultaneously and motion in the otherdirection simultaneously increases both the inductance and capacitance'of said reactance simultaneously.

ROBERT V. LANGMUIR. PH-ILL? H. PETERS, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,085,838 Usselman -July=6, 1937 2,341,345 Van Billiard "'Feb. 8,1944 2,367,681 K'arplus et al "Jan, 23,1945

FOREIGN PATENTS Number Country Date 109,093 Australia Nov. 13, 1939 

